1. Field of the Invention
The present invention relates to a pneumatic radial tire including a reinforcing belt of metal cords in a tread superior in durability at high speeds. More particularly it relates to a pneumatic radial tire including a center annular tread, a pair of sidewalls extending from ends of said tread and bead portions including a fiber cord radial carcass extending between the bead portions and having ends folded about the bead portions and affixed thereat. A belt layer is positioned of a plurality of metal cord layers above the carcass in the tread, of which metal cords are at angles 65.degree.-80.degree. to radial planes including a rotating axis of the tire and cross to the metal cords in the outer metal cord layers.
2. Description of the Prior Art
It has previously been suggested to reinforce a radial tire by a belt layer arranged on a carcass in a tread consisting of a plurality of metal cord layers with the cords at angles of 65.degree.-80.degree. to radial planes of the tire and crossed to the cords in other cord layers. Such a radial tire is superior in wear-resistance. However, it has been recognized that such a radial tire is not suitable for high speed driving because the tread is much heavier than that including a belt of fiber cord layers which frequently cause standing waves. During operation at low speeds, a deformation of a tread at a contact surface may be immediately restored by means of the tires inner pressure as soon as the deformed portion of the tread is out of contact with the road. However, when travelling at a higher speed, the centrifugal force may become sufficiently great so as to overcome the inner pressure until the centrifugal force causes waves at the deformed portion which propagate along the circumference of the tread. Such a phenomenon is referred to as "standing waves". When standing waves occur, heating rapidly increases to give rise to a peeling failure from heating, so that use of the tire is limited to lower speeds at which the standing wave will not be caused.
In order to avoid standing waves and to improve high speed performance, tires have been suggested in which a few of plies of fiber cords are wound such as nylon cords circumferentially over the entire width or a center zone or both ends of the outer periphery of metal belt layers to restrain the extension of the metal belt layers when travelling at high speeds.
The inventor of the invention of the present application has confirmed experimentally that such a construction for restraining the metal belt layers by the fiber cord layers remarkably improves the high speed performance but is unsatisfactory for preventing the standing waves. The inventor further noticed that as above described, standing waves result from incomplete restoration of the deformed tread in contact with the road and accordingly that it is advantageous for the tire that the effects of deformation of the tread be reduced. Upon further investigation of this consideration, the inventor surprisingly found that damper layers provided between belt plies of the ends of a belt layer serve to prevent standing waves as the result of reduced shearing strains in the belt plies above and under the damper layers. More over, there also results a remarkable increase in the restraining effect of the belt by the addition to the damper layers of high elastomeric rubber fillers reinforcing the zones from bead portions to the centers of the sidewalls which thereby not only further increases the deformation restraining effect on the belt layers but also the entire tire in conjunction with the damper layers so that the durability of the tire travelling at high speeds is remarkably improved.